The anterior divisions of the lumbar nerves, sacral nerves, and coccygeal nerve form the lumbosacral plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic. For descriptive purposes this plexus is usually divided into three parts: ...
The lumbar and sacral plexuses taken together. The fibres of the lumbosacral plexus originate in the lumbar and upper sacral spinal cord (l1 to s3) and innervate the lower extremities. ... (12 Dec 1998) ... 
the lumbar and sacral plexuses considered together, because of their continuous nature.
[n] - a nerve plexus formed by the ventral divisions of the coccygeal and sacral and lumbar nerves
Plexus (see separate entry) along the spinal cord at the level of the hind limbs; it is associated with the lumbosacral enlargement of the spinal cord.
noun a nerve plexus formed by the ventral divisions of the coccygeal and sacral and lumbar nerves; supplies the lower limbs and perineum and coccygeal area